In a tracked vehicle, especially a tank or the like which is subject to rough terrain and severe operating conditions, the track and wheel dynamics cause widely fluctuating track tension. Typically an idler wheel is provided to adjust tension but prior arrangements are limited in ability to control the tension. An ideal system would maintain, for all mobility scenarios, a track tension which is relatively uniform and of the lowest possible magnitude which provides proper guiding of the track throughout its entire path. Such an ideal system would maximize track and running gear life; aid in minimizing rolling resistance, which would improve drive train efficiency; assure a high level of mobility during aggressive and/or high speed maneuvering situations; and, in general, enhance the combat readiness, reliability, and maintenance characteristics of the vehicle over its life cycle.
Prior to this invention the track tensioning systems could be grouped into two basic types: fixed idler systems and movable idler systems. The fixed idler systems have an idler wheel initially adjusted for a desired static tension. The idler is then rigidly anchored to the hull. The movable idler systems have a track tensioning idler wheel connected to the forward road arm through a link whose length can be adjusted for a desired static tension. The geometry of the linkage is arranged so that as the road arm approaches its jounce, or uppermost, position the tensioning idler is moved forward. This motion attempts to maintain a uniform total periphery about all track-contacting elements; i.e. the road wheels, final drive sprocket, return rollers, and tensioning idler.
The tracks, of course, may operate in either a driving or a braking mode. In driving mode, the track is driven by the drive sprocket and applies a tractive effort to the ground which maintains or increases the track velocity. In braking mode the opposite occurs to decrease the track velocity. The tension in a given section of track varies greatly as the track moves around the drive sprocket, the tension being greater on the side of the sprocket nearest the road wheels when in driving mode and less during braking mode. Reverse travel and turning changes the tension conditions on one or both tracks. The negotiation of an obstacle at high speed accentuates the difference in tensions. Thus the tensions can vary widely and rapidly, if not controlled, and the wheels are affected as well.
For example, when the vehicle is traveling forward with both tracks driving, the rear wheels tend to compress to a degree dependent on the tractive effort. This reduces the total periphery of the track supporting members allowing the track to loosen and partially disengage from the tensioning idler. This condition can produce a thrown track if the vehicle should suddenly encounter an obstacle or attempt an abrupt steer maneuver.